A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to decrease the critical dimension of devices, a lithographic projection apparatus may be arranged with an EUV radiation source. The EUV radiation source may be, for example, a discharge plasma radiation source, in which a plasma is generated in a substance (for instance, a gas or vapor) between an anode and a cathode and in which a high temperature discharge plasma may be created by ohmic heating caused by a (pulsed) current flowing through the plasma. In addition to in-band EUV radiation, a practical EUV source also generates out-of-band radiation and debris, the latter of which severely limits the operational lifetime of reflective optics close to the radiation source. In the case of a Sn-based source, three types of debris can be distinguished:                slow atomic debris: thermalized atoms, i.e. with random direction and velocity according to the Maxwell distribution;        fast atomic debris: ions, neutrals and nano clusters with a high ballistic velocity substantially parallel to the EUV radiation emitted by the source;        micro-particles: micrometer-sized ballistic particles and droplets, also directed substantially parallel to the EUV radiation.        
Fast atomic debris reduce the reflectivity of the subsequent optics by etching, whereas slow atomic debris and micro-particles reduce the reflectivity by contaminating the surface. Either debris resistant components or debris mitigation or cleaning strategies should therefore be used in order to maintain sufficient output power in the EUV lithography tool.
PCT patent application publication WO 2005/025280 describes an EUV radiation source in which the anode and the cathode are formed by wheels that are wetted in a bath containing a liquid metal, such as Sn. Some of the debris is picked up by the thin film on the electrodes and transported back to the bath. Most of the debris however is directed towards the optics of the lithographic apparatus. This debris may be deflected by an additional electrode arrangement of thin metal sheets to which a voltage of several thousands of volts is applied.